Towards the end of our haunt we have a huge clown section then that leads them to the Curtains of Chaos. But after they find there way out get out, what should be the memory maker / big scare at the end that will leave them talking about it!?

Have some dummys, manniquins arranged on both sides of them and they have to walk between them to get out.
Have one live actor move ever so slightly, just as to garner some attention, as they hesitate and possibly back away, the second actor is already behind them in costume. All they have to do is just growl or make some small word or two loud enough for just that one person to hear, when they scream, jump back they will be in-range of the first "monster"
Done subtly , the others just a few feet back can be then played the same way because the sounds were quiet enough and the body movements small enough that the others back abit didn't see, hear or notice, of course adjusting the light lower helps this too.
Scaring people under bright, seemingly "show-All" illumination does set up a certain calmness that can then be taken full advantage of, though. (Fun! FUN!)

I'll see about getting a specific page number, but basically a little girl pops out of a hole in the wall and goes "boo!". Believe it or not, this would send virtually everyone running out screaming, often hitting the floor, and you know it was effective because the exit was right next to the entrance (like 5' away) and the customers running out screaming provided free entertainment to the people waiting in line.

They didn't know what it was that scared everyone, but they figured it must have been pretty intense. They were quite shocked to find out that they just had the crap scared out of them by a 10 year old girl going "boo!". Mind you, we're talking about grown adults looking their sh*t as well. Even big tough guys who don't scare easy would get a real jump.

Btw, this isn't hearsay. I worked in that haunt. I saw it in action personally. Very effective. What was really funny was watching an adult try to work that final scare, and naturally they thought that a little girl going "boo!" wasn't scary enough and so they would start writing there own material. Immediately you'd see the patrons going from running out screaming to "boy, that was lame" and just walk out. JB would be back there in a flash, grab the guy by the lapels just about and almost throw him out of the room. He'd then put another little girl in there and - bingo! - we're back to people running out screaming.

C.

*Incidentally, there was a little bit more than that happening behind the scenes . . .*